YAP1 oncogene is a context-specific driver for pancreatic ductal adenocarcinoma

Transcriptomic profiling classifies pancreatic ductal adenocarcinoma (PDAC) into several molecular subtypes with distinctive histological and clinical characteristics. However, little is known about the molecular mechanisms that define each subtype and how this correlates with clinical outcome. Mutant KRAS is the most prominent driver in PDAC, present in over 90% of tumors, but the dependence of tumors on oncogenic KRAS signaling varies between subtypes. In particular, squamous subtype PDACs are relatively independent of oncogenic KRAS signaling and typically display much more aggressive clinical behavior versus progenitor subtype PDACs. Here, we identified that YAP1 activation is enriched in the squamous subtype and associated with poor prognosis. Activation of YAP1 in progenitor subtype cancer cells profoundly enhanced malignant phenotypes and transformed progenitor subtype cells into squamous subtype. Conversely, depletion of YAP1 specifically suppressed tumorigenicity of squamous subtype PDAC tumors. Mechanistically, we uncovered a significant positive correlation between WNT5A expression and the YAP activation signature, and we demonstrated that WNT5A overexpression led to YAP activation and recapitulated YAP1-dependent but but Kras-independent phenotype of tumor progression and maintenance. Thus, our study identifies YAP1 oncogene as a major driver of squamous subtype PDAC and uncovers the role of WNT5A to drive PDAC malignancy via activation of the YAP pathway. Total RNA were obtained from PDAC cell line Pa04C expressing constitutive active Yap1 (S127A) or from a control vector